Chromium compound, catalyst system including the same, and method for trimerizing ethylene using the catalyst system

ABSTRACT

Disclosed herein are a chromium compound represented by Formula 1a or 1c and a catalyst system including the same, exhibiting superior catalytic activity in an olefin trimerization reaction:
 
[{CH 3 (CH 2 ) 3 CH(CH 2 CH 3 )CO 2 } 2 Cr(OH)]  [Formula 1a]
 
[{CH 3 (CH 2 ) 3 CH(CH 2 CH 3 )CO 2 } 2 Cr(OH)] 4 .2H 2 O.  [Formula 1c]

TECHNICAL FIELD

Embodiments of the present invention relate to a chromium compound, acatalyst system including the same, and a method of trimerizing ethyleneusing the catalyst system.

BACKGROUND ART

In 1994, Philips presented a catalyst system for preparing 1-hexene,etc. by trimerizing olefins, such as ethylene, particularly, a highlyactive and selective ethylene trimerization catalyst system using atrivalent chromium compound, a pyrrole compound, a non-hydrolyzedaluminum alkyl, and an aromatic hydrocarbon (unsaturated hydrocarbon)(U.S. Pat. No. 5,376,612). Subsequently, based on the catalyst system,1-hexene has been commercially produced since 2003. Among varioustrivalent chromium compounds, a catalyst system using tris(2-ethylhexanoate) chromium (III) (Cr(EH)₃, EH=O₂C₈H₁₅) exhibited superiorcatalytic activity. A catalyst system using Cr(EH)₃ has been intensivelyresearched and commercialized.

In the case of the catalyst system using Cr(EH)₃, an aromatichydrocarbon solvent may be prepared by, for example, adding a mixture oftriethylaluminum and ethylaluminum dichloride to an aromatic hydrocarbonsolvent (toluene, etc.), as a mixture of Cr(EH)₃ and2,5-dimethylpyrrole. In general, since trimerization of olefins iscarried out in an aliphatic hydrocarbon solvent such as cyclohexane, anaromatic hydrocarbon solvent of a prepared catalyst system is removedthrough vacuum suction and then the aromatic hydrocarbon solvent-removedcatalyst system is re-dissolved in an aliphatic hydrocarbon solvent suchas cyclohexane. Alternatively, the catalyst system using the preparedaromatic hydrocarbon is used in a trimerization reaction and, afterterminating the trimerization reaction, the aromatic hydrocarbon solventused to prepare the catalyst is isolated and removed. In addition, whena catalyst is prepared using Cr(EH)₃, a catalytic activation species isformed and thus a black precipitate is generated as a by-products,whereby a process of filtering the black precipitate is required (seeU.S. Pat. No. 5,563,312). Such processes of removing and filtering anaromatic hydrocarbon solvent, such as toluene, may be a roadblock tocommercialization. When the catalyst system is prepared in an aliphatichydrocarbon solvent, such as cyclohexane, in which trimerization occurs,to omit the process of removing an aromatic hydrocarbon solvent,thermostability of a prepared catalyst is decreased. Accordingly, acatalyst is inactivated during trimerization reaction or catalystselectivity is decreased, thus by-products, other than trimers, aregenerated in a large amount (see U.S. Pat. No. 5,563,312). Accordingly,in catalyst systems, etc. manufactured by Philips, aromatic hydrocarbons(unsaturated hydrocarbons) are included as essential components.

Therefore, there is a need for development of a raw material compoundwhich does not cause the production of by-products upon preparation of acatalyst and thus does not require a filtration process, etc. and allowsthe preparation of a catalyst system in an aliphatic hydrocarbonsolvent, and a catalyst system exhibiting superior catalytic activityupon ethylene trimerization.

DISCLOSURE Technical Problem

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide achromium compound having a novel structure.

It is another object of the present invention to provide a catalystsystem which allows a simple catalyst preparation process, exhibitssuperior catalytic activity upon an ethylene trimerization reaction, andincludes the chromium compound.

It is still another object of the present invention to provide anethylene trimerization reaction using the catalyst system.

The above and other objects can be accomplished by the present inventiondescribed below.

Technical Solution

An embodiment of the present invention relates to a chromium compoundrepresented by any one of Formulas 1a and 1b below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)], and  [Formula 1a][{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH)].  [Formula 1b]

The chromium compound may include a compound represented by Formula 1cbelow:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O.  [Formula 1c]

Another embodiment of the present invention relates to a catalyst systemincluding a reaction product of a chromium compound; an aluminumcompound; and a pyrrole compound, or an alumino-pyrrole compound.

The catalyst system of the embodiment may include a reaction product of:

a chromium compound represented by Formula 1 below;

an aluminum compound represented by Formula 3 below; and

a pyrrole compound represented by Formula 4 below:(R¹CO₂)₂Cr(OH)  [Formula 1]

wherein R¹ is a C₃ to C₃₀ alkyl group or a C₆ to C₄₀ aryl group;(R²)_(n)Al(X²)_(3-n)  [Formula 3]

wherein R² is a C₁ to C₂₀ hydrocarbon group, X² is a halogen atom, andan average value of n is 1 to 3; and

wherein R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atom or aC₁ to C₁₀ alkyl group.

In an embodiment of the catalyst system, the chromium compoundrepresented by Formula 1 may be a compound represented by any one ofFormulas 1a and 1b below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)], and  [Formula 1a][{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH)].  [Formula 1b]

In an embodiment of the catalyst system, the chromium compoundrepresented by Formula 1 may be a compound represented by Formula 1cbelow:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O  [Formula 1c]

The aluminum compound may be a mixture of triethylaluminum (Et₃Al) anddiethylaluminumchloride (Et₂AlCl) and the pyrrole compound representedby Formula 4 is 2,5-dimethylpyrrole.

In an embodiment of the catalyst system, a molar ratio of the chromiumcompound to the aluminum compound (Cr:Al) added upon preparation(reaction) may be 1:10 to 1:50.

In an embodiment of the catalyst system, a molar ratio of the chromiumcompound to the pyrrole compound (chromium compound:pyrrole compound)added upon preparation (reaction) may be 1:1 to 1:5.

In another embodiment, the catalyst system may include a reactionproduct of:

a chromium compound represented by Formula 1c below;

an aluminum compound represented by Formula 3 below; and

an alumino-pyrrole compound represented by Formula 5 below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O;  [Formula 1c](R²)_(m)Al(X²)_(3-n)  [Formula 3]

wherein R² is a C₁ to C₂₀ hydrocarbon group, X² is a halogen atom, andan average value of n is 1 to 3; and

wherein R² is a C₁ to C₂₀ hydrocarbon group and R³, R⁴, R⁵, and R⁶ areeach independently a hydrogen atom or a C₁ to C₁₀ alkyl group.

The aluminum compound is a mixture of triethylaluminum (Et₃Al) anddiethylaluminumchloride (Et₂AlCl), the alumino-pyrrole compoundrepresented by Formula 5 is a compound represented by Formula 5 whereinR² is an ethyl group, R³ and R⁶ are methyl groups, and R⁴ and R⁵ arehydrogen atoms.

In another embodiment of the catalyst system, a molar ratio of thechromium compound to the aluminum compound (Cr:Al) added uponpreparation (reaction) may be 1:10 to 1:50.

In another embodiment of the catalyst system, a molar ratio of thechromium compound to the alumino-pyrrole compound (chromiumcompound:alumino-pyrrole compound) added upon preparation (reaction) maybe 1:1 to 1:5.

In another embodiment, the catalyst system may include a catalystprecursor represented by Formula 2 below; and an aluminum compoundrepresented by Formula 3 below:

wherein R² is a C₁ to C₂₀ hydrocarbon group, X is R² or a halogen atom,and R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atom or a C₁ toC₁₀ alkyl group, and(R²)_(n)Al(X²)_(3-n)  [Formula 3]

wherein R² is a C₁ to C₂₀ hydrocarbon group, X² is a halogen atom, andan average value of n is 1 to 3.

In Formula 2, R² may be a methyl or ethyl group, X may be R² or achlorine atom, R³ and R⁶ may be methyl groups, and R⁴ and R⁵ may behydrogen atoms.

The aluminum compound may be a mixture of triethylaluminum (Et₃Al) anddiethylaluminumchloride (Et₂AlCl).

In the mixture, a molar ratio of the catalyst precursor to the aluminumcompound (Cr:Al) may be 1:10 to 1:50.

Another embodiment of the present invention relates to a catalystprecursor represented by Formula 2 below. The catalyst precursorrepresented by Formula 2 below is the same as the catalyst precursorrepresented by Formula 2 described above:

wherein R² is a C₁ to C₂₀ hydrocarbon group, X is R² or a halogen atom,and R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atom or a C₁ toC₁₀ alkyl group.

In another embodiment of the catalyst system, with regard to Formula 2,R² may be methyl or ethyl groups, X may be R² or a chlorine atom, R³ andR⁶ may be methyl groups, and R⁴ and R⁵ may be hydrogen atoms.

The catalyst systems according the aforementioned embodiments mayfurther include a hydrocarbon solvent.

Another embodiment of the present invention relates to a method ofpolymerizing olefins, the method including a step of preparing an olefinpolymer by bringing the catalyst system according to any one of theaforementioned embodiments into contact with a C₂ to C₁₀ olefin monomer.

The olefin monomer may be ethylene and the olefin polymer may be anolefin trimer.

Advantageous Effects

Embodiments of the present invention provide a chromium compound havinga novel structure. In addition, the present invention provides acatalyst system, which allows a simple catalyst preparation process,exhibits superior catalytic activity upon an ethylene trimerizationreaction, and includes the chromium compound, and a method of preparing1-hexene using the catalyst system.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the IR spectrum of a chromium compound preparedaccording to Preparation Example 3 of the present invention.

FIG. 2 illustrates the structure of a catalyst precursor (P1) preparedaccording to Preparation Example 6 of the present invention,investigated by single-crystal X-ray diffraction analysis.

FIG. 3 illustrates the structure of a catalyst precursor (P2) preparedaccording to Preparation Example 7 of the present invention,investigated by single-crystal X-ray diffraction analysis.

FIG. 4 illustrates a single-crystal X-ray diffraction analysis result ofan intermediate compound obtained by a catalyst system preparedaccording to Example 5 of the present invention.

BEST MODE

Hereinafter, the present invention is described in detail.

Chromium Compound

All of a chromium compound represented by Formula 1a below, a chromiumcompound represented by Formula 1b below, and embodiments thereof arecommonly designated as “chromium compounds,” unless specified otherwise.

Embodiments of the present invention relates to a chromium compoundhaving a novel structure represented by Formula 1a or 1b below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)], and  [Formula 1a][{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH)].  [Formula 1b]

The chromium compound represented by Formula 1a is a trivalent chromiumcompound including two 2-ethyl hexanoate ({CH₃(CH₂)₃CH(CH₂CH₃)CO₂})groups and one hydroxyl group (OH). When such a chromium compound isused in the catalyst system for polymerizing olefins, superior catalyticactivity is exhibited in an ethylene trimerization reaction.

The chromium compound represented by Formula 1b is a trivalent chromiumcompound including two 2-ethylbutanoate ({CH₃CH₂CH(CH₂CH₃)CO₂}) groupsand one hydroxyl group (OH). When such a chromium compound is used inthe catalyst system for polymerizing olefins, superior catalyticactivity is exhibited in an ethylene trimerization reaction.

In an embodiment, the chromium compound may include a compoundrepresented by Formula 1c below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(H)]₄.2H₂O  [Formula 1c]

The chromium compound represented by Formula 1c has a structure whereinfour trivalent chromium molecules having a structure of{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH) are combined with two water molecule.Accordingly, when the chromium compound represented by Formula 1c isused in the catalyst system for polymerizing olefins, superior catalyticactivity is exhibited in an ethylene trimerization reaction. Thechromium compound represented by Formula 1c may be prepared from, forexample, 2-ethylhexanoic acid, etc. through the aforementioned chromiumcompound preparation reaction. The 2-ethylhexanoic acid is cheap andindustrially mass-produced. Accordingly, Formula 1c may be moreeconomically prepared. In addition, since the chromium compound, etc.represented by Formula 1c has high solubility in aliphatic and aromatichydrocarbon solvents, a catalyst may be more easily prepared. Inaddition, a catalyst system prepared using the chromium compoundexhibits high catalytic activity.

The chromium compounds according to examples of the present inventionmay be prepared by reacting, for example, an aqueous solution of atrivalent chromium salt compound represented by Formula 6 below with anaqueous solution of a carboxylate alkali metal salt represented byFormula 7 below (hereinafter referred to as “reaction to prepare achromium compound”):Cr(X¹)₃  [Formula 6]wherein Formula 6, X¹ is a halogen atom, a nitrate ion (NO₃), or aperchlorate ion (ClO₄). The halogen atom may be, for example, a chlorineatom (Cl), an iodine atom (I), a fluorine atom (F), a bromine atom (Br),or the like.

In particular, examples of the trivalent chromium salt compoundrepresented by Formula 6 includes chromium chloride (CrCl₃) and ahydrate thereof (CrCl₃.H₂O), chromium nitrate (Cr(NO₃)₃) and a hydratethereof (Cr(NO₃)₃.H₂O), chromium perchlorate (Cr(ClO₄)₃) and a hydratethereof (Cr(ClO₄)₃.H₂O), and the like, but the present invention is notlimited thereto. In an embodiment, when, as the trivalent chromium saltcompound, a hydrate (for example, CrCl₃.H₂O, Cr(NO₃)₃.H₂O,Cr(ClO₄)₃.H₂O, or the like) is used, high solubility with respect towater is provided, whereby reactivity may be increased and economicefficiency may be provided.(R¹CO₂)M  [Formula 7]

In Formula 7, M is an alkali metal. The alkali metal may be, forexample, sodium (Na), potassium (K), lithium (Li), or the like. InFormula 7, R¹ is a C₃ to C₃₀ alkyl group or a C₆ to C₄₀ aryl group.

The alkali metal salt represented by Formula 7 may be easily obtained,for example, by reacting, a carboxylic acid (for example,2-ethylhexanoic acid, 2-ethylbutyric acid, or the like) with an alkalimetal hydroxide salt (NaOH, KOH, LiOH, or the like), in a predeterminedequivalent ratio, in water.

In particular, the carboxylate alkali metal salt represented by Formula7 below may be a compound represented by Formula 7a or 7b below:{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}M, and  [Formula 7a]{CH₃CH₂CH(CH₂CH₃)CO₂}M.  [Formula 7b]

In Formulas 7a and 7b, M is an alkali metal. The alkali metal may be,for example, sodium (Na), potassium (K), lithium (Li), or the like.

More particularly, the carboxylate alkali metal salt represented byFormula 7a or 7b may be, for example, sodium 2-ethyl hexanoate, sodium2-ethylbutanoate, or the like, but the present invention is not limitedthereto. In an embodiment, when sodium 2-ethyl hexanoate or sodium2-ethylbutanoate is used, the compound by represented Formula 1a, 1b or1c may be advantageously prepared and a raw material may be easilyobtained, thereby reducing the unit cost of production.

In reaction to prepare the chromium compound (reaction of an aqueoussolution of a trivalent chromium salt compound with an aqueous solutionof the carboxylate alkali metal salt), a reaction temperature may be 20°C. to 100° C., for example 50° C. to 100° C. Particularly, thetemperature may be 80° C. to 95° C. In the reaction, an equivalent ratioof an alkali metal salt of a carboxylic acid (for example,2-ethylhexanoic acid, 2-ethylbutanoic acid, or the like) to thetrivalent chromium salt compound (1 equivalent) may be 1:3 to 1:4,particularly 1:3 to 1:3.5 or 1:3 to 1:3.2. Within the range, thechromium compound may be obtained in high yield.

When the reaction to prepare the chromium compound is performed withinthe temperature range and the equivalent ratio range, a chromiumcompound and a by-product, a carboxylic acid (for example,2-ethylhexanoic acid, 2-ethylbutanoic acid, or the like), may begenerated.

In the reaction to prepare the chromium compound, a hydrocarbon solvent(for example, methylcyclohexane, mineral spirits, etc.) may be furtherincluded. The chromium compound prepared by the reaction and 1equivalent of a carboxylic acid (for example, 2-ethylhexanoic acid,2-ethylbutanoic acid, or the like), as a by-product of the reaction, haslow solubility with respect to water, but high solubility with respectto a hydrocarbon solvent. Accordingly, when, during the reaction toprepare a chromium compound, the hydrocarbon solvent is additionallyadded, the generated chromium compound and the by-product, carboxylicacid (for example, 2-ethylhexanoic acid, 2-ethylbutanoic acid, or thelike), are dissolved in a layer of the hydrocarbon solvent and otherby-products and unreactive products remain in an aqueous solution layer,whereby isolation and purification may be facilitated.

For example, when a hydrocarbon solvent is further added, a hydrocarbonsolvent layer is collected after the chromium compound preparationreaction and then the collected hydrocarbon solvent layer is washed withan alkaline aqueous solution, whereby a by-product, a carboxylic acid(for example, 2-ethylhexanoic acid, 2-ethylbutanoic acid, or the like),may be extracted by an alkaline aqueous solution layer and thus removed.By such a method, a chromium compound may be easily obtained in solutionwith a hydrocarbon solvent. A resultant solution may be directly used toprepare the catalyst system. Alternatively, as needed, the resultantsolution may be used in a powder form after removing a solvent therefromthrough distillation.

The hydrocarbon solvent may be, for example, a C₄ to C₂₀ aliphatichydrocarbon solvent, a C₆ to C₂₀ aromatic hydrocarbon solvent, a mixturethereof, or the like. In particular, the aliphatic hydrocarbon solventmay be, for example, isobutane, pentane, hexane, heptane, octane,nonane, decane, cyclohexane, methylcyclohexane, etc. and the aromatichydrocarbon solvent may be, for example, benzene, toluene, xylene,mesitylene, ethylbenzene, cumene, etc.

The structure of the chromium compound prepared according to the methodmay be confirmed by analyzing elemental analysis data, observing O—Hstretching signals at 3,630 cm⁻¹ of an IR spectrum, etc.

In addition, by measuring the mass of an obtained chromium compound,with respect to the mass of an added trivalent chromium salt compound,and the mass of 1 equivalent carboxylic acid (for example,2-ethylhexanoic acid, 2-ethylbutanoic acid, or the like) generated as aby-product, the production of a chromium compound having the compositionof Formula 1a, 1b or 1c may be additionally confirmed.

In addition, when the chromium compound is prepared using chromiumchloride (CrCl₃) as a trivalent chromium salt compound, the structure ofthe chromium compound may be additionally verified by titrating theamount of chlorine ions (Cl⁻) remaining in an aqueous solution layerwith silver nitrate (AgNO₃) or analyzing the acidity of the aqueoussolution layer.

In an embodiment, when the acidity of an aqueous solution layer isanalyzed and, as a result, is neutral in the case in which a chromiumcompound is prepared using chromium chloride (CrCl₃) as a trivalentchromium salt compound, it can be confirmed that the prepared chromiumcompound is composed of a composition including{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH), {CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH) or[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.H₂O).

In addition, the shape and structure of the prepared chromium compoundmay be investigated from a molecular weight, which is calculated fromfreezing point depression measured in benzene, and elemental analysisdata.

In an embodiment, the chromium compound represented by Formula 1c mayhave, more particularly, a structure represented by Formula 1d below:

wherein R¹ is an ethylpentyl group (CH₃(CH₂)₃CH(CH₂CH₃)—). The chromiumcompound represented by Formula 1 d has an adamantane structure.

A chromium compound having such an adamantane structure may be preparedaccording to, for example, the method of Example 5 described below. Thepresence of the chromium compound having the adamantane structure may beinferred from the structure of a cluster compound composed of fourchromium atoms (FIG. 4), which is determined by analyzing the structureof a single crystal of an intermediate compound, which is partiallyprecipitated by a catalyst solution prepared according to Example 5,using an X-ray diffraction method.

When the chromium compound represented by Formula 1c([{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O) has an adamantane structurerepresented by Formula 1d, the shape of the chromium compound may bestably maintained. In this case, a method of preparing the chromiumcompound is more reliable, thus being efficient and having economicfeasibility. In addition, the chromium compound with the adamantanestructure has high solubility and, when dissolved, low viscosity,thereby having superior handling property and superior uniformity in areaction.

In addition, the structure of the compound represented by Formula 1c,i.e., [{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O, which has a shape whereinfour {CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH) molecules are combined with twowater molecule, may be determined by molecular weight and elementalanalysis data calculated from a value of freezing point depressionmeasured in benzene.

Structural stability of the chromium compound represented by Formula 1dincluding two water molecules may be determined by confirming that thewater molecules are not removed from the chromium compound at all, whenthe chromium compound is dissolved in xylene to remove two watermolecules coordinated therein and then refluxed at 160° C. for 10 hoursby means of a Dean-Stark device. In addition, it was confirmed thatmolecular weights were not changed by calculating IR spectrum results,elemental analysis data, and measured values of freezing pointdepression in benzene, before and after the dehydration reaction. In thecase of Cr(EH)₃ used in the preparation of conventional Philipscatalysts, the composition of Cr(EH)₃ is different according to thebatches of prepared compounds, and thus, there are problems regardingreliability and reproducibility. However, in the case of the chromiumcompound of Formula 1d provided in the present invention,reproducibility and reliability may be easily secured, upon preparationof the chromium compound and the catalyst, due to a stable structure ofthe chromium compound.

In an embodiment, the aforementioned chromium compounds may becoordinated with a neutral ligand such as tetrahydrofuran,dimethylsulfoxide, or pyridine, but the present invention is not limitedthereto. Such neutral ligands may be easily decoordinated by a Lewisacidic aluminum compound upon preparation of a catalyst system describedbelow. In addition, when a chromium compound reacts with an aluminumcompound described below, a carboxylate group of the chromium compoundis exchanged with a hydrocarbon group (R²—) of the aluminum compound,the carboxylate group may be released from the chromium compound.

Catalyst System Including Chromium Compound

Another embodiment of the present invention relates to a catalyst systemincluding the aforementioned chromium compound. The catalyst system mayinclude, in addition to the chromium compound, an aluminum compound anda pyrrole compound; or an aluminum compound and an alumino-pyrrolecompound. When such a catalyst system is used in an olefinpolymerization reaction, high activity is exhibited.

In an embodiment, the a catalyst system includes a reaction product of achromium compound represented by Formula 1 below; an aluminum compoundrepresented by Formula 3 below; and a pyrrole compound represented byFormula 4 below. Since such a catalyst system do not produceprecipitates upon catalyst preparation, a filtration process is notrequired and thus a catalyst may be easily prepared. In addition, such acatalyst system is very useful in an ethylene trimerization reaction.(R¹CO₂)₂Cr(OH)  [Formula 1]

In Formula 1, R¹ is a C₃ to C₃₀ alkyl group or a C₆ to C₄₀ aryl group.

In particular, the alkyl group may be a C₃ to C₁₀ linear, branched, orcyclic alkyl group. More particularly, the alkyl group may be a C₅ to C₇branched alkyl group. In particular, the aryl group may be a C₆ to C₁₂aryl group.

for example, R¹ may be an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a sec-butyl group, an n-pentyl group, anisopentyl group, a neopentyl group, a 1,2-dimethylpropyl group, ann-hexyl group, a cyclohexyl group, a 1,3-dimethylbutyl group, a1-isopropylpropyl group, a 1-ethylpropyl group, a 1,2-dimethylbutylgroup, an n-heptyl group, a 1,4-dimethylpentyl group, a2-methyl-1-isopropylpropyl group, a 1-ethyl-3-methylbutyl group, a1-ethylpentyl group, an n-octyl group, a 2-ethylhexyl group, a3-methyl-1-isopropylbutyl group, a 2-methyl-1-isopropylbutyl group, aphenyl group, a naphthyl group, or the like, but the present inventionis not limited thereto.

In an embodiment, the chromium compound represented by Formula 1 mayinclude particularly one or more of compounds represented by Formula 1aor 1b below:[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]  [Formula 1a][{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH)]  [Formula 1b]

In an embodiment, the chromium compound includes a compound representedby Formula 1c below.[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O  [Formula 1c]

In an embodiment of the catalyst system, the aluminum compound is acompound represented by Formula 3 below:(R²)_(n)Al(X²)_(3-n)  [Formula 3]

wherein R² is a C₁ to C₂₀ hydrocarbon group, X² is a halogen atom, andan average value of n is 1 to 3.

The hydrocarbon group may be, particularly, a C₁ to C₂₀ alkyl group, aC₁ to C₁₅ alkyl group, a C₁ to C₁₀ alkyl group, or a C₁ to C₅ alkylgroup. The alkyl group may have, for example, a linear, branched, orcyclic structure. More particularly, the hydrocarbon group may be, forexample, a methyl group, an ethyl group, a propyl group, an isobutylgroup, or the like.

The halogen atom may be, for example, a chlorine atom (Cl), an iodineatom (I), a fluorine atom (F), a bromine atom (Br) and n may be, forexample, 2 to 3.

In an embodiment, the aluminum compound may be a single compound or amixture of aluminum compounds, n values of which are different, but thepresent invention is not limited thereto. In particular, the aluminumcompound may be an aluminum compound ((R²)₃Al) represented by Formula 3,wherein n is 3, and/or an aluminum compound ((R²)₂Al(X²)) represented byFormula 3, wherein n is 2. Among these, triethylaluminum (Et₃Al) anddiethylaluminumchloride (Et₂AlCl) represented by Formula 3, wherein R²is an ethyl group, are massively used as a promoter of a Ziegler-Nattacatalyst in the industry and are cheap, thereby being used to increaseeconomic efficiency. But the present invention is not limited thereto.The (R²)₂Al(X²) may be obtained by reacting (R²)₃Al with various organicand inorganic substances including a halogen.

In addition, a mix ratio (molar ratio) of (R²)₃Al:(R²)₂Al(X²) may be1:0.5 to 1:2, for example, 1:1, but the present invention is not limitedthereto.

In an embodiment of the catalyst system, the aluminum compoundrepresented by Formula 3 may be a mixture of triethylaluminum (Et₃Al)and diethylaluminumchloride (Et₂AlCl). In this case, a mix ratio (molarratio) of triethylaluminum (Et₃Al):diethylaluminumchloride (Et₂AlCl) maybe 1:0.5 to 1:2, for example, 1:1. Within this range, reactionefficiency of the catalyst system may be increased without an excessiveremainder of an unreacted aluminum compound.

A molar ratio of the chromium compound to the aluminum compound (Cr:Al),which are added upon preparation (reaction) of the catalyst system, maybe 1:3 to 1:100, for example, 1:10 to 1:50, particularly 1:10 to 1:40.Within this range, a highly active catalyst system may be realized whileincreasing economic efficiency. In this case, 1-hexene, as an ethylenetrimer, may be obtained in high yield and in high purity.

In the catalyst system, the aluminum compound may participate in areaction of forming an active catalyst species by reacting with thechromium compound and the pyrrole compound. In addition, a portion ofthe aluminum compound may remove a catalytic poison, such as water oroxygen included in a solvent and a monomer, upon catalyst systempreparation or olefin polymerization (trimerization). Since the amountsof water, oxygen, etc. included in a solvent and a monomer may differ ona case-by-case basis, an optimal addition amount of the aluminumcompound may be differently set according to each case.

In addition, when the catalyst system is used in olefin polymerization,an aluminum compound may be separately added to an olefin polymerizationreaction solvent, regardless of the catalyst system, to remove water,oxygen, etc. In this case, the amount of the aluminum compoundseparately added to the olefin polymerization reaction solvent is notincluded in the molar ratio.

In an embodiment of the catalyst system, a pyrrole compound reactingwith the chromium compound represented by Formula 1 or the aluminumcompound represented by Formula 3 may be a compound represented byFormula 4 below:

wherein R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atom or aC₁ to C₁₀ alkyl group.

In Formula 4, the alkyl group may have, for example, a carbon number of1 to 8, 1 to 6, or 1 to 4 and a linear, branched, or cyclic structure.In particular, the alkyl group may be, for example, a methyl group, anethyl group, a propyl group, an isobutyl group, or the like.

More particularly, the pyrrole compound represented by Formula 4 may be,for example, a pyrrole (R³, R⁴, R⁵, and R⁶ of Formula 4 are hydrogenatoms), a pyrrole compound (Formula 4, R³ is a hydrogen atom and one ormore of R⁴, R⁵, and R⁶ is a C₁ to C₁₀ alkyl group), or the like, but thepresent invention is not limited thereto.

In an embodiment of the catalyst system, the pyrrole compoundrepresented by Formula 4 may be 2,5-dimethylpyrrole wherein R³ and R⁶ ofFormula 4 are methyl groups. In this case, the cost of a raw material islow and a highly active catalyst system may be realized.

In the catalyst system, a molar ratio of the chromium compound to thepyrrole compound (chromium compound:pyrrole compound) added uponpreparation (reaction) may be 1:1 to 1:10, for example, 1:1 to 1:5.Particularly, the molar ratio may be 1:1 to 1:3. Within this range, thecatalyst system exhibits superior activity, thereby obtaining highlypure 1-hexene, as an ethylene trimer, in high yield.

In an embodiment, an alumino-pyrrole compound represented by Formula 5described below may be prepared by reacting the chromium compoundrepresented by Formula 1, the aluminum compound represented by Formula3, and the pyrrole compound represented by Formula 4 in a hydrocarbonsolvent, through the catalyst system.

In another embodiment, the alumino-pyrrole compound represented byFormula 5 described below may be prepared, through the catalyst system,by preparing a mixture including the aluminum compound represented byFormula 3 and the pyrrole compound represented by Formula 4 and thenreacting the mixture with the chromium compound in a hydrocarbonsolvent.

In another embodiment, the catalyst system includes a reaction productof the chromium compound represented by Formula 1c; the aluminumcompound represented by Formula 3; and the alumino-pyrrole compoundrepresented by Formula 5 described below. Such a catalyst system is veryuseful in an ethylene trimerization reaction. In addition, such acatalyst system allows preparation of a catalyst in an aliphatichydrocarbon solvent, thus being more useful.

The chromium compound represented by Formula 1c and the aluminumcompound represented by Formula 3 are described in the aforementionedembodiments.

In Formula 5, R² is a C₁ to C₂₀ hydrocarbon group and R³, R⁴, R⁵, and R⁶are each independently a hydrogen atom or a C₁ to C₁₀ alkyl group.

In Formula 5, R² may be, particularly, a hydrocarbon group, for example,a C₁ to C₂₀ alkyl group, a C₁ to C₁₅ alkyl group, or a C₁ to C₁₀ or a C₁to C₅ alkyl group.

In Formula 5, R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atomor, for example, a C₁ to C₈, a C₁ to C₆, or a C₁ to C₄ alkyl group.

In Formula 5, the alkyl group may have a linear, branched, or cyclicstructure. More particularly, the alkyl group may be, for example, amethyl group, an ethyl group, a propyl group, an isobutyl group, or thelike.

In the alumino-pyrrole compound represented by Formula 5 of anembodiment of the catalyst system, R³ and R⁶ may be methyl groups, R⁴and R⁵ may be hydrogen, and R² may be an ethyl group. When such analumino-pyrrole compound is used, the catalyst system exhibits highactivity.

In an embodiment, the alumino-pyrrole compound may be prepared by amethod of reacting, for example, the pyrrole compound represented byFormula 4 with (R²)₃Al; or a method of forming the pyrrole compoundrepresented by Formula 4 into an N-lithio-pyrrole compound using n-BuLi,etc. and then reacting the N-lithio-pyrrole compound with (R²)₂AlCl.Here, the reaction solvent may be diethyl ether, or the like. In thiscase, aluminum of the compound represented by Formula 5 may becoordinated with diethyl ether. Since diethyl ether coordinated withaluminum is easily decoordinated upon the preparation of the catalystsystem, the presence or absence of the coordinated diethyl ether doesnot greatly affect the activity of the prepared catalyst system.

In an embodiment, a molar ratio of the chromium compound to thealumino-pyrrole compound (chromium compound:alumino-pyrrole compound)may be 1:1 to 1:10, for example 1:1 to 1:5. Particularly, the molarratio may be 1:1 to 1:3. Within this range, the catalyst system exhibitssuperior activity and high-purity 1-hexene, as an ethylene trimer, maybe obtained in high yield.

In an embodiment, the catalyst system may be prepared (reacted) at −30to 50° C., for example 0 to 40° C. Particularly, the catalyst system maybe prepared at 15 to 35° C. Within this range, the catalyst system maybe obtained in high yield.

According to the embodiments, the catalyst system may further include ahydrocarbon solvent. When the hydrocarbon solvent is included, thereaction product of the catalyst system may be present as a uniformsolution dissolved in the hydrocarbon solvent.

In addition, the catalyst system manufactured by Philips, as describedin the Background Art, essentially requires an aromatic hydrocarbonsolvent. However, the catalyst system according to the embodiments ofthe present invention has superior solubility with respect to ahydrocarbon solvent and exhibits high activity in an aliphatichydrocarbon solvent. Accordingly, the catalyst system may be prepared inan aliphatic hydrocarbon solvent during the ethylene trimerizationreaction, whereby an aromatic hydrocarbon solvent removal process and afiltration process may be omitted.

The hydrocarbon solvent may be, for example, a C₄ to C₂₀ aliphatichydrocarbon solvent, a C₆ to C₂₀ aromatic hydrocarbon solvent, a mixturethereof, or the like. The aliphatic hydrocarbon solvent may be, forexample, isobutane, pentane, hexane, heptane, octane, nonane, decane,cyclohexane, methylcyclohexane, or the like. Particular examples of thearomatic hydrocarbon solvent include benzene, toluene, xylene,mesitylene, ethylbenzene, cumene, and the like. The ethylenetrimerization reaction is carried out in an aliphatic hydrocarbonsolvent. Accordingly, when the same aliphatic hydrocarbon solvent as thesolvent used in the ethylene trimerization reaction is used to preparethe catalyst system, isolation and purification processes, after thereaction, may be easily performed.

The aforementioned embodiment of the catalyst system may be obtained by,for example, contacting the chromium compound represented by Formula 1,the aluminum compound represented by Formula 3, and a pyrrole compoundrepresented by Formula 4 below in a hydrocarbon solvent and reacting thesame. In particular, the embodiment of the catalyst system may beprepared by adding the aluminum compound to a mixture prepared by addingthe chromium compound and the pyrrole compound in the hydrocarbonsolvent and reacting the same.

The aforementioned another embodiment of the catalyst system may beobtained by, for example, reacting the chromium compound represented byFormula 1c, the aluminum compound represented by Formula 3, and analumino-pyrrole compound represented by Formula 5 below in a hydrocarbonsolvent.

In another embodiment, the catalyst system may include a mixture of acatalyst precursor represented by Formula 2 below; and an aluminumcompound represented by Formula 3.

In the catalyst system, the catalyst precursor may be a compoundrepresented by Formula 2 below:

In Formula 2, R² is a C₁ to C₂₀ hydrocarbon group and R³, R⁴, R⁵, and R⁶are each independently a hydrogen atom or a C₁ to C₁₀ alkyl group.

In Formula 2, R² may be, particularly, a hydrocarbon group, for example,a C₁ to C₂₀ alkyl group, a C₁ to C₁₅ alkyl group, or a C₁ to C₁₀ or a C₁to C₅ alkyl group.

In Formula 2, R³, R⁴, R⁵, and R⁶ are each independently a hydrogen atomor, for example, a C₁ to C₈, a C₁ to C₆, or a C₁ to C₄ alkyl group.

In Formula 2, the alkyl group may have a linear, branched, or cyclicstructure. More particularly, the alkyl group may be, for example, amethyl group, an ethyl group, a propyl group, an isobutyl group, or thelike.

In the catalyst precursor represented by Formula 2 of an embodiment ofthe catalyst system, R² may be a methyl group or an ethyl group, X maybe the same as R² or a chlorine atom, R³ and R⁶ may be methyl groups,and R⁴ and R⁵ may be hydrogen atoms. When such a catalyst precursor isused, the catalyst system exhibits high activity.

In another embodiment of the catalyst system, the aluminum compound isthe same as the aluminum compound represented by Formula 3 described inthe aforementioned embodiments.

In an embodiment of the catalyst system, a molar ratio of the catalystprecursor represented by Formula 2 to the aluminum compound representedby Formula 3 (Cr:Al) may be 1:3 to 1:100, for example 1:10 to 1:50, 1:10to 1:40, 1:10 to 1:30 or 1:10 to 1:20. Within this range, a highlyactive catalyst system may be realized while increasing economicefficiency. In this case, high-purity 1-hexene, as an ethylene trimer,may be obtained in high yield. In addition, the amount of an unreactedreaction product is decreased and thus the efficiency of the catalystsystem may be further increased.

An embodiment of the catalyst system includes a mixture of the catalystprecursor represented by Formula 2 below and the aluminum compoundrepresented by Formula 3. The mixture may be produced during, forexample, a reaction process of the catalyst system according to theaforementioned embodiment or the catalyst system according to anotherembodiment.

Catalyst Precursor

Another embodiment of the present invention relates to the catalystprecursor represented by Formula 2. Such a catalyst precursor may bederived from the chromium compound represented by Formula 1. Detaileddescription for the catalyst precursor is the same as that for theaforementioned catalyst system.

In an embodiment, the catalyst precursor may be obtained by, forexample, a preparation method using reaction in the catalyst systemaccording to the aforementioned embodiments; a preparation method usinga reaction of the chromium compound represented by Formula 1 with thecompound represented by Formula 5; or the like, but the presentinvention is not limited thereto. For example, the catalyst precursormay be synthesized as described in Preparation Example 6 or 7 below.

Method of Polymerizing Olefins

Another embodiment of the present invention relates to a method ofpolymerizing olefins using the aforementioned catalyst system.

The method includes a step of preparing an olefin polymer (trimer) bybringing the catalyst system into contact with a C₂ to C₁₀ olefinmonomer.

The catalyst system of the present invention may be present in, as wellas a uniform solution, a carrier-included form, an insoluble particleform in a carrier, or the like. Accordingly, the olefin polymerization(trimerization) may be a liquid-phase, slurry-phase, bulk-phase, orgas-phase polymerization reaction. In addition, each polymerizationreaction condition may be variously modified according to the states ofused catalysts (uniform or non-uniform state (supported type)),polymerization methods (solution polymerization, slurry polymerization,and gas phase polymerization), desired polymerization results, orpolymer types. Such modifications may be easily made by those skilled inthe art. When the polymerization is performed in a liquid or slurryphase, a hydrocarbon solvent or an olefin monomer itself may be used asa medium. The hydrocarbon solvent may be a C₄ to C₂₀ aliphatichydrocarbon solvent, a C₆ to C₂₀ aromatic hydrocarbon solvent, a mixturethereof, or the like. The aliphatic hydrocarbon solvent may be, forexample, isobutane, pentane, hexane, heptane, octane, nonane, decane,cyclohexane, methylcyclohexane, or the like. Particular examples of thearomatic hydrocarbon solvent include benzene, toluene, xylene,mesitylene, ethylbenzene, cumene, and the like. In general, the olefinpolymerization (trimerization) reaction may be carried out in analiphatic hydrocarbon solvent considering environmental problems. Inaddition, when isolation from an olefin polymer, as a product producedafter reaction, is considered, a difference between the boiling point ofa used hydrocarbon solvent and the boiling point of the product ispreferably 10 to 50° C. For example, when the olefin monomer is ethyleneand the product is 1-hexene (boiling point: 63° C.), production costsare low and cyclohexane having a boiling point of 80.74° C. ormethylcyclohexane having a boiling point of 101° C. may be used.

In an embodiment, examples of the olefin monomer include ethylene,propylene, 1-butene, 1-hexene, 1-octene, 1-decene, a mixture thereof,and the like. Preferably, ethylene is used alone.

In the olefin polymerization (trimerization) method of the presentinvention, a use amount of the catalyst system is not specificallylimited. However, since the catalyst system of the present inventionexhibits high activity, the catalyst system may be used in a smallamount, compared to conventional catalyst systems, to cause a reaction.In an embodiment, the olefin polymerization method is solutionpolymerization, the catalyst system is added at a molar concentration(based on chromium) of 0.01 mmol/L to 0.1 mmol/L, for example, 0.01mmol/L to 0.03 mmol/L, with respect to the hydrocarbon solvent, and thenreaction is performed for thirty minutes to one hour by continuouslyadding an olefin monomer, such as ethylene. Accordingly, the volume of aresultant solution may be about two times an initial volume due to thegenerated olefin polymer (trimer), such as 1-hexene. For reference, inthe case of a published patent document of Philips, catalytic activityis lower than that of the catalyst system of the present invention andthus a polymerization reaction is performed at a catalyst concentrationof about 0.25 mmol/L (see U.S. Pat. No. 5,856,257).

In addition, upon the olefin polymerization (trimerization) of thepresent invention, a temperature may be changed according to reactionsubstances, reaction conditions, and the like. The temperature may be 0°C. to 150° C., for example, 60° C. to 130° C. For example, thepolymerization may be performed in a batch, semi-continuous, orcontinuous process. The polymerization may be carried out through two ormore steps, reaction conditions of which are different.

Hereinafter, the constitution and functions of the present invention aredescribed in more detail with reference to examples of the presentinvention. However, the following examples are merely provided aspreferred embodiments and, therefore, the present invention is notlimited to the examples.

EXAMPLE Preparation Example 1: Preparation of Chromium CompoundRepresented by Formula 1a

2-ethylhexanoic acid (2.44 g, 16.9 mmol) was fed into a 1-neck flask,and then NaOH (0.68 g, 16.9 mmol) dissolved in distilled water (13 ml)was added thereto, thereby preparing sodium 2-ethyl hexanoate.

Subsequently, mineral spirits (5 ml) were additionally added thereto toform two phases. While stirring the resultant mixture at 95° C.,hydrated chromium (III) chloride (CrCl₃.H₂O, 1.50 g, 96%, 5.40 mmol)dissolved in distilled water (1 ml) was slowly added thereto. A reactionwas rapidly performed and a product was dissolved into an organic layer.After allowing reaction for 2 hours, an aqueous layer became transparentand all of generated products were dissolved into an organic layer.Accordingly, the organic layer appeared navy blue.

The aqueous solution layer collected after the two-phase reaction wasalmost neutral. In addition, after the two-phase reaction, silvernitrate (AgNO₃) was added to the aqueous solution layer and thus themass of precipitated silver chloride (AgCl) was measured. The mass ofprecipitated silver chloride (AgCl) was 2.28 g. From this data, it canbe confirmed that Cl ions of added CrCl₃ are almost completely removed(calculated value: 2.32 g).

Only the organic layer was collected, washed with distilled water (10ml) twice, and subjected to vacuum distillation (0.3 mmHg, 130° C.),thereby removing the mineral spirits and by-products, 2-ethylhexanoicacid and remaining moisture. As a result, 1.94 g of a navy bluesolid-type chromium compound represented by Formula 1a was obtained(yield: 101%). An aqueous NaOH solution was added to a mixture of2-ethylhexanoic acid and mineral spirits outflowed during the vacuumdistillation and thus sodium 2-ethyl hexanoate was formed. The formedsodium 2-ethyl hexanoate was extracted into an aqueous solution layerand then hydrochloric acid was added to the aqueous solution layer atthe same time. Reproduced 2-ethylhexanoic acid was extracted withdiethyl ether and the mass thereof was measured. The measured mass was0.80 g. From this result, it was confirmed that 1.0 equivalent(calculated value: 0.78 g) of 2-ethylhexanoic acid with respect to theadded trivalent chromium salt compound was produced as a by-product{Anal. calc. (C₁₆H₃₁CrO₅): C, 54.07; H, 8.79. Found: C, 54.67; H, 9.03}.

The chromium compound obtained according to Preparation Example 1 wassubjected to IR spectrum analysis. As a result, an O—H stretching signalwas observed at 3630 cm⁻¹.

Preparation Example 2: Preparation of Chromium Compound Represented byFormula 1b

A navy blue solid-type chromium compound represented by Formula 1b wasprepared in the same manner as in Preparation Example 1, except that2-ethylbutyric acid (16.9 mmol) was used instead of 2-ethylhexanoic acid(C, 48.52; and H, 7.85, and, with respect to{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH), C, 48.15; and H, 7.75).

The compound prepared according to Preparation Example 2 was dissolvedin benzene and then the molecular weight thereof was measured using afreezing point depression method. As a result, the molecular weight was3330 and about 11 {CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH) molecules was present inbenzene as an assembly (i.e., [{CH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH)]₁₁).

As an elemental analysis result, the structure of the compound preparedaccording to Preparation Example 2 was identical to that ofCH₃CH₂CH(CH₂CH₃)CO₂}₂Cr(OH), not including a water molecule.

When the compound prepared according to the Preparation Example 2 wasdissolved in xylene and then refluxed at 160° C. for 10 hours, the colorof the compound changed from navy blue to green and elemental analysisdata values were also changed (C, 50.85; H, 7.96).

Preparation Example 3: Preparation of Chromium Compound Represented byFormula 1c

2-ethylhexanoic acid (2.44 g, 16.9 mmol) was fed into a 1-neck flask,and then NaOH (0.68 g, 16.9 mmol) dissolved in distilled water (13 ml)was added thereto, thereby preparing sodium 2-ethyl hexanoate.Subsequently, methylcyclohexane (7 ml) was additionally added thereto toform two phases. While stirring the resultant mixture at 95° C.,hydrated chromium (III) chloride (CrCl₃.H₂O, 1.50 g, 96%, 5.40 mmol)dissolved in distilled water (1 ml) was slowly added thereto. A reactionwas rapidly performed and a product was dissolved into an organic layer.After allowing reaction for 2 hours, an aqueous layer became transparentand all of generated products were dissolved into an organic layer.Accordingly, the organic layer appeared viscous navy blue and an aqueouslayer became transparent.

The pH of the aqueous layer was neutral. In addition, it could beconfirmed that, when considering that the weight of precipitated silverchloride (AgCl) was 2.28 g upon addition of a large amount of silvernitrate (AgNO₃, 3.03 g, 17.8 mmol), almost all of Cl ions of CrCl₃ wereremoved (calculated value: 2.32 g).

The organic layer was diluted by additionally adding hexane (5 ml).Subsequently, only the organic layer was collected and NaOH (0.22 g,5.40 mmol) dissolved in distilled water (3 ml) was added thereto,followed by strongly stirring for 30 minutes. 2-ethylhexanoic acid (1equivalent with respect to trivalent chromium salt compound) produced asa by-product and in a sodium salt form in an aqueous layer was removed.The organic layer was only collected and water remaining therein wasremoved with magnesium sulfate, followed by removing an organic solventtherefrom by vacuum drying (0.3 mmHg) at room temperature. As a result,a navy blue solid-type chromium compound([{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O) was obtained in an amount of1.94 g. When calculated based on the structure of[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O, yield was 98%.

The IR spectrum of the prepared chromium compound is illustrated inFIG. 1. As a result of the IR spectrum analysis, it can be confirmedthat an O—H stretching signal is observed at 3630 cm⁻¹. After dissolvingthe chromium compound in benzene, the molecular weight thereof wasmeasured using a freezing point depression method. As a result, themolecular weight was 1580 which is close to the molecular weight of thetetramer. In addition, as an elemental analysis result, the structure ofchromium compound was identical to that of[{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O (C, 52.48; and H, 8.88, and, acalculated theoretical value of [{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH)]₄.2H₂O,C, 52.73; and H, 8.85).

When the chromium compound prepared according to Preparation Example 3was dissolved in xylene and then refluxed at 160° C. for 10 hours, navyblue was maintained with little color change. In addition, it wasconfirmed that elemental analysis data values hardly changed and thus astable shape was maintained.

Preparation Example 4: Preparation of Alumino-Pyrrole Compound (B1)

Under an inert atmosphere (nitrogen), triethylaluminum (7.20 g, 63.1mmol) dissolved in toluene (60 ml) was fed into a 1-neck flask, and then2,5-dimethylpyrrole (1.50 g, 15.8 mmol) was additionally added thereto,followed by stirring at room temperature for five hours. Next, tolueneand unreacted triethylaluminum were removed therefrom by vacuumdistillation (0.3 mmHg, 70° C.), thereby obtaining 2.80 g of a pyrrolealuminum compound (1-(diethylalumino)-2,5-dimethylpyrrole) in which N—Alcovalent bonds were formed. According to this method, an alumino-pyrrolecompound (B1) which had the structure represented by Formula 5 in whichR² was an ethyl group, R³ and R⁶ were methyl groups, R⁴ and R⁵ werehydrogen was prepared. A result of ¹H NMR analysis is as follows: yield:99%, ¹H NMR (C₆D₆): ä 5.51 (s, 2H, Ar—H), 2.01 (s, 6H, CH₃), 1.35 (t,J=8 Hz, 6H, CH₃), 0.35 (q, J=8 Hz, 4H, CH₂) ppm}.

Preparation Example 5: Preparation of Alumino-Pyrrole Compound (B2)

Under an inert atmosphere (nitrogen), 2,5-dimethylpyrrole (3.00 g, 31.5mmol) was dissolved in diethyl ether (30 ml) in a 1-neck flask and aresultant solution was cooled to −78° C. Subsequently, n-butyllithium(13.7 g, 31.5 mmol, 1.6 M hexane solution) was slowly added thereto.After stirring overnight at room temperature, the mixture was re-cooledto −78° C. and then dimethylaluminumchloride (Me₂AlCl, 20.6 g, 31.5mmol, 1.0 M hexane solution) was slowly added thereto. After stirringovernight, filtration was performed and, as a result, a yellow solutionwas obtained. Subsequently, the solution was subjected to vacuum drying,thereby obtaining 6.67 g of a (1-(dimethylalumino)-2,5-dimethylpyrrole)compound. According to this method, an alumino-pyrrole compound (B2)which had the structure represented by Formula 5 and in which R², R³ andR⁶ were methyl groups and R⁴ and R⁵ were hydrogen was prepared. As aresult of ¹H NMR analysis, it was confirmed that 1 equivalent of diethylether was attached to the alumino-pyrrole compound (B2) (yield: 94%). ¹HNMR (C₆D₆): ä 6.23 (s, 2H, CH), 3.15 (q, J=7.2 Hz, 4H, CH₂), 2.44 (s,6H, CH₃), 0.55 (t, J=6.8 Hz, 6H, CH₃), −0.33 (s, 6H, CH₃) ppm}.

Preparation Example 6: Preparation of Catalyst Precursor (P1)

Under an inert atmosphere (nitrogen), the chromium compound (Formula 1c,200 mg, 0.563 mmol) prepared according to Preparation Example 3dissolved in pentane (9.0 ml) was fed into a 25 ml 1-neck flask, andthen the alumino-pyrrole compound (B2, 380 mg, 1.69 mmol) of PreparationExample 5 dissolved in toluene (1.0 ml) was slowly added thereto, suchthat two solution layers were formed. According to this method, acatalyst precursor (P1) which had the structure represented by Formula 2and in which R², X, R³ and R⁶ were methyl groups and R⁴ and R⁵ werehydrogen was prepared.

In the state in which two solution layers were formed as describedabove, crystals were precipitated while allowing slow reaction for oneweek (143 mg, yield: 65%). The structure of an obtained single crystalwas analyzed by an X-ray diffraction method. A result is illustrated inFIG. 2.

Preparation Example 7: Preparation of Catalyst Precursor (P2)

Under an inert atmosphere (nitrogen), lithium diisopropylamide (LiNiPr₂,1.50 g, 14.0 mmol) dissolved in toluene (15 ml) was fed into a 1-neckflask, and then diethylaluminum chloride (Et₂AlCl, 0.844 g, 7.00 mmol)was added thereto at room temperature slowly, thereby preparing amixture. After stirring for six hours at room temperature, generatedlithium chloride was filtered out. Subsequently, an obtained solutionwas subjected to vacuum drying, thereby obtaining 1.64 g ofLiAlEt₂(NiPr₂)₂ as a white solid {yield: 80%, ¹H NMR (C₆D₆): ä 3.14 (m,4H, CH), 1.56 (t, J=8.0 Hz, 6H, CH₃), 1.01 (d, J=6.4 Hz, 24H, CH₃), 0.34(q, J=7.6 Hz, 4H, CH₂) ppm. ¹³C NMR (C₆D₆): ä 46.06, 26.25, 11.11, −8.18ppm}. LiAlEt₂(NiPr₂)₂ (1.00 g, 3.42 mmol) was dissolved in toluene (15ml) and then cooled to −30° C., followed by adding CrCl₃(THF)₃ (1.28 g,3.42 mmol) thereto. During stirring for eight hours at room temperature,the color of the solution changed from dark green to blue. A solvent wasremoved from the solution by means of a vacuum pump and then hexane (20ml) was added thereto. Precipitated lithium chloride was removed throughfiltration and cooling to −30° C. was performed, thereby obtainingcrystals (770 mg). Crystals (100 mg, 0.245 mmol) obtained according tothe method were dissolved in toluene (1 ml), and then the compound (132mg, 0.735 mmol) represented by Formula 5, which was prepared accordingto Preparation Example 4, dissolved in toluene (1 ml) was added theretoat room temperature.

According to this method, a catalyst precursor (P2) which had thestructure represented by Formula 2 and in which R² was an ethyl group, Xwas a chlorine atom, R³ and R⁶ were methyl groups, and R⁴ and R⁵ werehydrogen was prepared.

A resultant reaction solution was stirred for one hour, and thendiffused with pentane overnight, thereby decreasing solubility and thusprecipitating crystals (90 mg). An obtained single crystal compound wassubjected to an X-ray diffraction analysis. An analyzed structure isillustrated in FIG. 3.

Hereinafter, the following examples and comparative examples wereperformed under an inert atmosphere (nitrogen).

Example 1: Preparation of a Catalyst System (1)

The alumino-pyrrole compound (B1, 81 mg, 0.45 mmol) synthesized inPreparation Example 4 was dissolved in methylcyclohexane (1 ml) and aresultant mixture was fed into a 1-neck flask. In addition,triethylaluminum (137 mg, 1.20 mmol) and diethylaluminum chloride (145mg, 1.20 mmol) were dissolved in methylcyclohexane (2 ml) and then fedinto the 1-neck flask, thereby preparing a mixture.

The chromium compound (Formula 1a, 53 mg, 0.15 mmol) prepared inPreparation Example 1 was dissolved in methylcyclohexane (1 ml) and thenadded to the mixture, followed by allowing reaction. As a result, acatalyst system was prepared as a dark green transparent solution inwhich hardly any precipitate was present (concentration: 63 mmolchromium/g-solution).

Example 2: Preparation of Catalyst System (2)

A catalyst system was prepared as a dark green transparent solution inthe same manner as in Example 1, except that the chromium compound(Formula 1b) prepared in Preparation Example 2 was used instead of thechromium compound (Formula 1a) prepared in Preparation Example 1(concentration: 63 mmol chromium/g-solution).

Example 3: Preparation of Catalyst System (3)

The chromium compound (Formula 1c, 110 mg, 0.30 mmol) prepared inPreparation Example 3 was dissolved in toluene (3 ml). Subsequently,2,5-dimethylpyrrole (86 mg, 0.90 mmol) was added thereto and atemperature was lowered to 0° C. To a resultant mixture, a toluenesolution (2 ml) in which triethylaluminum (377 mg, 3.30 mmol) anddiethylaluminum chloride (289 mg, 2.40 mmol) were dissolved and mixedwas slowly added. When reaction was allowed at 0° C. for one hour, adark yellow solution in which hardly any precipitate was present wasformed. It could be confirmed that, after temperature was highlyelevated, the dark yellow solution changed into a dark orange solution(concentration: 50 μmol chromium/g-solution).

Example 4: Preparation of Catalyst System (4)

The alumino-pyrrole compound (B1, 81 mg, 0.45 mmol) represented byFormula 5 (R²=ethyl group, R³═R⁶=methyl group, R⁴═R⁵=hydrogen)synthesized in Preparation Example 4 was dissolved in methylcyclohexane(1 ml) was fed into a 1-neck flask. Triethylaluminum (137 mg, 1.20 mmol)and diethylaluminum chloride (145 mg, 1.20 mmol) were dissolved inmethylcyclohexane (2 ml) and fed into the 1-neck flask, therebypreparing a mixture. The chromium compound (Formula 1c, 55 mg, 0.15mmol) prepared in Preparation Example 3 was dissolved inmethylcyclohexane (1 ml) and added to the prepared mixture, followed byallowing reaction. As a result, a catalyst system was prepared as a darkgreen transparent solution in which a precipitate was hardly present(concentration: 50 mmol chromium/g-solution).

Example 5: Preparation of Catalyst System (5)

A catalyst system was prepared in the same manner as in Example 4,except that the alumino-pyrrole compound represented by Formula 5 (B2,R²=methyl group, R³═R⁶=methyl group, R⁴═R⁵=hydrogen) prepared inPreparation Example 5 was used instead of the alumino-pyrrole compoundrepresented by Formula 5 (B1, R²=ethyl group, R³═R⁶=methyl group,R⁴═R⁵=hydrogen) prepared in Preparation Example 4, and trimethylaluminumand dimethylaluminum chloride were used instead of triethylaluminum anddiethylaluminum chloride (concentration: 50 μmol chromium/g-solution).When the prepared catalyst system was stored for one month at roomtemperature, a single crystal of a reaction intermediate was partiallyprecipitated. The structure of the precipitated single crystal wasanalyzed by an X-ray diffraction method. As a result, a cluster compoundcomposed of four chromium atoms was determined as illustrated in FIG. 4.

Example 6: Preparation of Catalyst System (6) Including CatalystPrecursor

The compound (10 mg, 25.5 μmol) represented by Formula 2 (P1,R²═X=methyl group, R³═R⁶=methyl group, R⁴═R⁵=hydrogen) synthesized inPreparation Example 6 was added to methylcyclohexane (0.3 ml) in a1-neck flask. Triethylaluminum (137 mg, 1.20 mmol) and diethylaluminumchloride (145 mg, 1.20 mmol) were dissolved in methylcyclohexane (0.7ml) and then fed into the 1-neck flask. As a result, a catalyst systemwas prepared as a dark green transparent solution (concentration: 50μmol chromium/g-solution).

Example 7: Preparation of Catalyst System (7) Including CatalystPrecursor

A catalyst system was prepared as a dark green transparent solution inthe same manner as in Example 6, except that the compound represented byFormula 2 (P2, R²=ethyl group, X=chlorine, R³═R⁶=methyl group,R⁴═R⁵=hydrogen) prepared in Preparation Example 7 was used instead ofthe compound represented by Formula 2 (P1, R²═X=methyl group,R³═R⁶=methyl group, R⁴═R⁵=hydrogen) prepared in Preparation Example 6(concentration: 50 μmol chromium/g-solution).

Comparative Example 1: Preparation of Catalyst System of Philips

According to a method disclosed in U.S. Pat. No. 5,856,257, a catalystsystem was prepared. Tris(2-ethyl hexanoate) chromium (III) (Cr(EH)₃)(145 mg, 0.30 mmol) was dissolved in toluene (3 ml). Subsequently,2,5-dimethylpyrrole (86 mg, 0.90 mmol) was added thereto and atemperature was lowered to 0° C. To the resultant mixture, a toluene (2ml) solution in which triethylaluminum (377 mg, 3.30 mmol) anddiethylaluminum chloride (289 mg, 2.40 mmol) were dissolved and mixedwas slowly added. When reaction was allowed at 0° C. for one hour, ablack precipitate was formed. The formed precipitate was removed throughfiltration, thereby obtaining a transparent dark orange catalyst systemsolution (concentration: 50 mmol chromium/g-solution).

Comparative Example 2: Preparation of Catalyst System of Philips

A catalyst system was prepared in the same manner as in ComparativeExample 1, except that chromium (III) (Cr(EH)3) manufactured by the samecompany but having a different serial number was used.

Comparative Example 3: Preparation of Catalyst System

A catalyst system was prepared in the same manner as in ComparativeExample 1, except that methylcyclohexane, instead of toluene. A blackprecipitate was filtered and thus a catalyst system was prepared as adark green solution (concentration: 50 mmol chromium/g-solution).

Example 8: Ethylene Trimerization Reaction Using Catalyst System ofExample 3

Methylcyclohexane (20 ml) and triethylaluminum (0.024 mmol), asscavengers, were fed into a high-pressure polymerization reactor in adry box. Subsequently, the high-pressure polymerization reactor wastaken out of the dry box and the temperature thereof was elevated to 90°C. The catalyst system (0.25 μmol) prepared in Example 3 was weighed andmethylcyclohexane was added thereto, such that a total volume of aresultant solution became 2 ml. Since the catalyst was used in a verysmall amount, triethylaluminum (8 equivalents with respect to chromium)and diethylaluminum chloride (8 equivalents with respect to chromium)were added thereto as scavengers, and then a catalyst solution wasaspirated by a syringe and injected into the reactor. Subsequently,ethylene was injected at a pressure of 50 bar and polymerization wasperformed for 30 minutes. The temperature of the reactor was rapidlylowered and then an ethylene gas was vented and removed from thereactor. 5 ml of ethanol and 5 ml of 10% hydrochloric acid were added tothe reactor, thereby terminating the reaction. A portion of a resultantsample was taken and subjected to gas chromatography. The amount of1-hexene generated through the gas chromatography was measured. Inaddition, the amount of a solid-type polymer formed by filtering theentire resultant solution was measured. A result is summarized in Table1 below.

Example 9 to 12: Ethylene Trimerization Reaction Using Catalyst Systemof Each of Examples 4 to 7

Ethylene polymerization (trimerization) was carried out in the samemanner as in Example 8, except that the catalyst system prepared in eachof Examples 4 to 7, instead of the catalyst system prepared in Example3, was weighed and used in an amount summarized in Table 1 (0.25 μmol to1.00 μmol). After terminating the reaction, a portion of a sample wastaken and subjected to gas chromatography. The amount of 1-hexenegenerated through the gas chromatography was measured. In addition, theamount of a solid-type polymer formed by filtering the entire resultantsolution was measured. A result is summarized in Table 1 below.

Example 13: Ethylene Trimerization Reaction Using Catalyst System ofExample 1

Ethylene polymerization (trimerization) was carried out in the samemanner as in Example 8, except that the catalyst system prepared inExample 1 was used in an amount of 0.250 μmol. After terminating thereaction, a portion of a sample was taken and subjected to gaschromatography. The amount of 1-hexene generated through the gaschromatography was measured. In addition, the amount of a solid-typepolymer formed by filtering the entire resultant solution was measured.A result is summarized in Table 1 below.

Example 14: Ethylene Trimerization Reaction Using Catalyst System ofExample 2

Ethylene polymerization (trimerization) was carried out in the samemanner as in Example 8, except that the catalyst system prepared inExample 2, instead of the catalyst system prepared in Example 1, wasused in an amount of 0.50 μmol. After terminating the reaction, aportion of a sample was taken and subjected to gas chromatography. Theamount of 1-hexene generated through the gas chromatography wasmeasured. In addition, the amount of a solid-type polymer formed byfiltering the entire resultant solution was measured. A result issummarized in Table 1 below

Comparative Example 4: Ethylene Trimerization Reaction Using CatalystSystem of Comparative Example 1

Methylcyclohexane (20 ml) and triethylaluminum (0.024 mmol) were fedinto a high-pressure polymerization reactor in a dry box as scavengers.Subsequently, the high-pressure polymerization reactor was taken out ofa dry box and the temperature thereof was elevated to 90° C. Thecatalyst system (solution, 1.00 μmol) prepared in Comparative Example 1was weighed and taken and methylcyclohexane was added thereto, such thata total volume of a resultant solution became 2 ml. A catalyst solutionwas aspirated by a syringe and injected into the reactor. Subsequently,ethylene was injected at a pressure of 50 bar and polymerization wasperformed for 30 minutes. The temperature of the reactor was rapidlylowered and then an ethylene gas was vented and removed from thereactor. 5 ml of ethanol and 5 ml of 10% hydrochloric acid were added tothe reactor, thereby terminating the reaction. A portion of a resultantsample was taken and subjected to gas chromatography. The amount of1-hexene generated through the gas chromatography was measured. Inaddition, the amount of a solid-type polymer formed by filtering theentire resultant solution was measured. A result is summarized in Table2 below.

Comparative Example 5: Ethylene Trimerization Reaction Using CatalystSystem of Comparative Example 2

Ethylene polymerization (trimerization) was performed in the same manneras in Comparative Example 4, except that the catalyst system solutionprepared in Comparative Example 2 was used instead of the catalystsystem prepared in Comparative Example 1. After terminating thereaction, a portion of a sample was taken and subjected to gaschromatography. The amount of 1-hexene generated through the gaschromatography was measured. In addition, the amount of a solid-typepolymer formed by filtering the entire resultant solution was measured.A result is summarized in Table 2 below.

Comparative Example 6: Ethylene Trimerization Reaction (2) UsingCatalyst System of Comparative Example 1

Ethylene polymerization (trimerization) was performed in the same manneras in Comparative Example 4, except that the catalyst system prepared inComparative Example 1 was used in an amount of 2.00 μmol. Afterterminating the reaction, a portion of a sample was taken and subjectedto gas chromatography. The amount of 1-hexene generated through the gaschromatography was measured. In addition, the amount of a solid-typepolymer formed by filtering the entire resultant solution was measured.A result is summarized in Table 2 below.

Comparative Example 7: Ethylene Trimerization Reaction Using CatalystSystem of Comparative Example 3

Ethylene polymerization (trimerization) was performed in the same manneras in Comparative Example 4, except that the catalyst system prepared inComparative Example 3 was used in an amount of 2.00 μmol. Afterterminating the reaction, a portion of a sample was taken and subjectedto gas chromatography. The amount of 1-hexene generated through the gaschromatography was measured. In addition, the amount of a solid-typepolymer formed by filtering the entire resultant solution was measured.A result is summarized in Table 2 below.

Preparation Example 8: Preparation of Chromium Compound Having StructureRepresented by Formula 1

An experiment was performed in the same manner as in Preparation Example3, except that 2,2-dimethylpropionic acid was used instead of2-ethylhexanoic acid. After synthesizing a compound, vacuum suction wasperformed at 120° C. As a result, a solvent and 2,2-dimethylpropionicacid, as a by-product, were removed and a gel-type product was obtained.

Preparation Example 9: Preparation of Chromium Compound Having StructureRepresented by Formula 1

An experiment was performed in the same manner as in Preparation Example1, except that heptanoic acid was used instead of 2-ethylhexanoic acid.After synthesizing a compound, vacuum suction was performed at 120° C.As a result, a solvent and heptanoic acid, as a by-product, were removedand a gel-type product was obtained.

Preparation Example 10: Preparation of Chromium Compound HavingStructure Represented by Formula 1

An experiment was performed in the same manner as in Preparation Example1, except that benzoic acid was used instead of 2-ethylhexanoic acid.During a reaction process, a navy blue gel was obtained.

Preparation Example 11: Preparation of Chromium Compound HavingStructure Represented by Formula 1

An experiment was performed in the same manner as in Preparation Example1, except that cyclohexanecarboxylic acid was used instead of2-ethylhexanoic. During a reaction process, a navy blue gel wasobtained.

Property Evaluation Methods

(1) Activity (unit: Kg(1-hexene)/g(catalyst(Cr))/hr): After measuringthe mass of obtained 1-hexene, activity was obtained by dividing themeasured mass by the amount of an added catalyst.

(2) Stability evaluation of compound: the compound prepared in each ofPreparation Example 1 and Preparation Example 3 was dissolved in xyleneand then refluxed at 160° C. for 10 hours to evaluate stability

TABLE 1 Examples 8 9 10 11 12 13 14 Catalyst system Example ExampleExample Example Example Example Example 3 4 5 6 7 1 2 Amount of catalyst0.25 0.25 1.00 1.00 1.00 0.25 0.50 (μmol) Amount of 6.9 7.1 5.6 12.4 6.47.1 9.6 obtained 1-hexene (g) Activity (Kg(1- 1,070 1,100 220 500 2601,100 770 hexene)/g(Cr)/h) Dimer C4 (wt %) 4.26 0.70 0.24 3.21 0.86 0.010.10 Trimer C6 (wt %) 88.08 94.12 92.38 88.08 93.60 93.06 93.14 TetramerC8 (wt %) 0.29 0.48 0.39 0.39 0.32 0.48 0.35 Pentamer C10 7.37 4.70 6.998.32 5.22 5.50 6.41 (wt %) Content of 1- 99.21 98.42 98.77 98.2 98.5698.98 99.07 hexene in trimer (wt %) Amount of 27 27 35 17 6 27 28obtained PE (mg)

TABLE 2 Comparative Examples 4 5 6 7 Catalyst system Compar- Compar-Compar- Compar- ative ative ative ative Example 1 Example 2 Example 1Example 3 Amount of catalyst 1.00 1.00 2.00 2.00 (μmol) Amount ofobtained 7.2 3.2 15.1 11.9 1-hexene (g) Activity (Kg(1- 280 120 290 230hexene)/g(Cr)/h) Dimer C4 (wt %) 0.52 1.00 0.01 0.03 Trimer C6 (wt %)92.97 93.04 92.08 92.36 Tetramer C8 (wt %) 0.38 0.64 0.34 0.41 PentamerC10 (wt %) 6.08 5.33 7.57 7.20 Content of 1-hexene 98.85 97.78 98.5199.01 in trimer (wt %) Amount of obtained 32 11 25 28 PE (mg)

From these results, it can be confirmed that the catalyst systems ofExamples 8 to 14 including the chromium compound represented by Formula1 or the chromium-based catalyst precursor represented by Formula 2exhibit similar or greatly increased catalytic activity (up to fourtimes) compared to the catalyst systems of Comparative Examples 4 to 7using Cr(EH)₃, whereby the cost of a catalyst can be greatly reduced.

In particular, activity degrees in Examples 8, 9, 13, and 14 includingthe chromium compound represented by Formula 1 of the present inventionare remarkably high, compared to Comparative Examples 4 to 7 usingCr(EH)₃.

In Examples 10 to 12, activity, an attainment rate of a trimer, thecontent of 1-hexene in the trimer, and the like are similar to those ofComparative Example 4 to 7, but a removal process of an aromatichydrocarbon solvent is not required. In addition, the unit cost of a rawmaterial is low and economic efficiency is superior. In particular, inthe cases of Example 10 to 12, a catalyst is used in a much smalleramount, but when comparing Examples 10 to 12 and Comparative Examples 6and 7, a similar result is exhibited.

From these results, it can be confirmed that, in the cases of thecatalyst systems of Example 8 to 14, a catalyst may be prepared in analiphatic hydrocarbon solvent, an aromatic hydrocarbon solvent removalprocess of trimerizing ethylene in the aliphatic hydrocarbon solvent isnot required, and a filtration process is not required since aprecipitate is not generated upon preparation of the catalyst.Accordingly, it can be confirmed that a preparation process of thecatalyst system is simple and may be easily performed.

In addition, when the stabilities of the compounds of PreparationExample 1 and Preparation Example 3, in which the chromium compoundaccording to the present invention is prepared, are compared, it can beconfirmed that the stability of the compound of Preparation Example 3 issuperior compared to that of the compound of Preparation Example 1. Fromthis result, it can be confirmed that both catalyst systems includingthe chromium compounds of Preparation Example 1 and Preparation Example3 exhibit high catalytic activity, but the chromium compound having thestructure represented by Formula 1c prepared in Preparation Example 3exhibits higher stability. In particular, it can be confirmed that thechromium compound of Preparation Example 3 exhibits superior solubilitywith respect to a hydrocarbon solvent and thus has very suitablecharacteristics for being applied to the catalyst system.

In addition, through Preparation Example 8 to 11, preparation of variousembodiments of the chromium compound represented by Formula 1 includedin the present invention were confirmed.

Those of ordinary skill in the art may easily carry out simpleapplications and modifications based on the foregoing teachings withinthe scope of the present invention, and these modified embodiments mayalso be within the scope of the present invention.

The invention claimed is:
 1. A chromium compound represented by Formula1a:{CH₃(CH₂)₃CH(CH₂CH₃)CO₂}₂Cr(OH).  [Formula 1a]